This invention relates generally to electronic governors for internal combustion engines. More specifically the invention relates to a new and unique electronic interface for interfacing the governor to a microcomputer in such a manner that the microcomputer, acting through the interface, exercises closed loop control over the governor.
Electronic controls can be used to operate the fuel injection equipment of a diesel engine in a manner that provides better performance than that which is attainable with older technology of the type employing flyweight governors, mechanical stops and aneroids. One particular implementation of an injection system that is electronically controlled includes replacing the mechanical rack actuating mechanism and stops of an in-line jerk-pump with a microcomputer-controllable proportional solenoid actuator assembly. This assembly comprises an actuator that is positioned in accordance with the extent to which its solenoid is energized. The proportional solenoid is selectively energized in accordance with the fuel deliver control signal to in turn selectively position the fuel rack via the actuator, and correspondingly modulate the fuel flow from the injection pump into the engine.
A feedback loop is closed around the proportional solenoid actuator. It includes an eddy current device which has a measuring coil that senses the rack position and feeds this information back to the microcomputer. Because the eddy current device is temperature-sensitive, a separate reference coil is located in proximity to the measuring coil, and a signal derived from this reference coil is used to modify the signal derived from the measuring coil so that the signal fed back to the microcomputer can be temperature-compensated.
In conventional implementations of this type of system, analog electrical signals from the sensor are supplied to the microcomputer, or microprocessor, which must then convert them into digital form for use in carrying out the necessary computations. The computations of the microcomputer are converted into an appropriate control signal for operating the proportional solenoid.
Because the fuel injection equipment of a diesel engine is located on the engine, placement of the microcomputer in proximity to the injection equipment poses a problem. The temperature sensitive nature of LSI (large scale integration) microelectronic circuitry, that is typical of a microcomputer, makes such placement undesirable unless elaborate thermal protection provisions are employed for it. Yet, if the microcomputer is remotely located in a less hostile area where less elaborate protection is required, analog signals must be transmitted to and from the injection equipment over conductors which may be exposed to electrical interference or noise adversely affecting the analog signals. Thus, these contradictory objectives beset the implementation of a microcomputer control for an electronic engine governor mechanism.
The present invention relates to a novel and unique approach for providing microcomputer control of an electronic engine governor in a way which overcomes the aforementioned difficulties. This approach is embodied in an electronic interface module that is provided between the microcomputer and the fuel injection equipment. The module is constructed for the most part of discrete electronic components and is constructed and packaged in a manner such that it can be mounted in close proximity to the fuel injection equipment without serious detriment. At the same time the microcomputer can be placed in a less hostile environment where temperature ranges and conditions are typically not as extreme as in proximity to the engine. Moreover, the interface module comprises circuits that provide for the transmission of signals between itself and the microcomputer that are digital rather than analog in nature, so that electrical noise that may be picked up by the wiring which connects the module with the microcomputer has a less detrimental effect on the signals than if they were analog.
A further feature of the invention relates to the manner in which the electronic circuitry of the interface module is arranged to interact with the proportional solenoid and the eddy current sensor. Although pulse width modulation of the proportional solenoid is not broadly novel, one of the unique features of the invention is that the eddy current sensor is connected in pulse width modulating circuitry that produces sensor information as a pulse width modulated signal. In particular the pulse width modulated eddy current sensor signal is synchronized with the pulse width modulated fuel deliver signal that operates the proportional solenoid. In other words, the present invention, through this novel interface module, provides from the eddy current sensor to the microcomputer relatively noise immune digital feedback which is synchronized with the relatively noise immune pulse width modulated fuel deliver control signal issued from the microcomputer to the proportional solenoid.
A still further feature involves the use of pulse stretcher circuitry in the interface module that stretches the pulse width modulated signal from the eddy current sensor. By so stretching this signal, and supplying the stretched signal directly to the microcomputer, the microcomputer can read the signal by using it to gate a counter for counting clock pulses. This improves the resolution of reading the feedback signal and enhances the ultimate accuracy of the system in comparison to prior systems. Pulse stretchers are used with both the reference coil and the measuring coil of the eddy current sensor so that the waveform to the microcomputer comprises two stretched components, one for the measurement coil, the other for the reference coil.
The stretching of the respective pulses derived from the measurement coil and the reference coil respectively is performed in such a manner that the stretched reference pulse component of the signal to the microcomputer is always in a predetermined relationship to the stretched measurement pulse component. This relationship can even be achieved where the unstretched pulse relationships are not always necessarily consistent. For example, while the unstretched measurement pulse will normally be wider than the unstretched reference pulse, certain conditions may result in the unstretched reference pulse being wider. In such a case, consistency in the relationship of the stretched pulses is attained by stretching the reference pulse and the measurement pulse by different factors. The microcomputer performs the necessary computation on the two stretched pulse signal components so that temperature influences which could adversely affect the reading are compensated for in the fuel deliver control signal that is issued to the governor.
The foregoing features, advantages, and benefits of the invention, along with the additional ones, will be seen in the ensuing description and claims which should be considered in conjunction with the accompanying drawings. The drawings disclose a preferred embodiment of the invention according to the best mode contemplated at the present time in carrying out the invention.